A planetary gear unit is commonly known as a power transmission mechanism for reducing or increasing a rotational speed of a rotative power source inputted from a driving power source. The planetary gear unit includes a ring gear having internal teeth, a sun gear with external teeth, and a planetary gear disposed between the ring gear and the sun gear to mesh with the gears.
With the planetary gear unit of this type, a speed increasing/decreasing ratio is high using fewer gears and it is possible to transmit high torque. Thus, the planetary gear unit is widely used as a speed change gear or a speed increasing/decreasing gear. For instance, it is used as a step-up gear in a wind turbine generator. Herein, the wind turbine generator is formed by a hub to which blades are attached, a nacelle for housing the step-up gear and a generator, and a tower for supporting the nacelle. In the wind turbine generator of this type, the planetary gear unit is used as the step-up gear to convert the rotational speed into a speed appropriate for generating power, during transmission of a turning force of the blade to the generator.
As a technique related to this, Patent Literature 1 discloses a gearbox for a wind power generation facility provided with a planetary gear unit. The gearbox is a planetary gear unit having a carrier rotating with a main shaft coupled to the blade and a plurality of planetary pins attached to the carrier. Planetary gears are attached to the planetary pins via slide bearings and a ring gear and a sun gear mesh with the planetary gears. As a result, the rotation of the main shaft causes the planetary gears to both rotate around its axis and revolve around the sun gear so as to output the increased rotation to the sun gear side.
As shown in FIG. 10A and FIG. 10B, in the planetary gear unit 50, the slide bearing 53 is normally attached to an inner periphery of a shaft hole of the planetary gear 52. FIG. 10A is a perspective illustration of the conventional planetary gear and the slide bearing. FIG. 10B is a cross-sectional view of FIG. 10A taken in an axial direction. From a perspective of maintaining slidability between the planetary pin 51 and the slide bearing 53 and also enhancing a life of the bearing, lubricating oil is supplied to a space between the inner periphery of the slide bearing 53 and the outer periphery of the planetary pin 51 to form an oil film on the bearing surface. However, with the use of the slide bearing 53 of this type in the planetary gear unit 50, it is unavoidable that the slide bearing 53 rotating integrally with the planetary gear rotates at a low speed and the planetary pin 51 contacts the slide surface of the slide bearing 53. Therefore, the slide surface of the slide bearing 53 is often made of resin material such as PEEK resin and Teflon (registered trademark) having high heat resistance.